Three estimates of heritability are available from the half-sib pedigree design: the sire, dam an... more Three estimates of heritability are available from the half-sib pedigree design: the sire, dam and genotypic estimates. Because of its significantly smaller standard error, the genotypic estimate is preferred provided that there are no non-additive effects that inflate the estimate. I present two methods to test for such effects: these are a t-test of the paired sire and dam pseudovalues from the jackknife procedure and the likelihood ratio test from the animal model. Both methods are shown to be valid tests for significant dominance and/or maternal effects. SPLUS coding for the implementation of the jackknife method is provided. Unless sample sizes are very large, the power of the tests is low and hence caution is advised in the use of the genotypic estimate following a nonsignificant test. An approximate power analysis can be done using the data from the jackknife method but the estimated power is typically a substantial underestimate of the true power and its use is not recommended.
The International Union for Conservation of Nature (IUCN) Red List provides a globally-recognized... more The International Union for Conservation of Nature (IUCN) Red List provides a globally-recognized evaluation of the conservation status of species, with the aim of catalysing appropriate conservation action. However, in some parts of the world, species data may be lacking or insufficient to predict risk status. If species with shared ecological or life history characteristics also tend to share their risk of extinction, then ecological or life history characteristics may be used to predict which species may be at risk, although perhaps not yet classified as such by the IUCN. Statistical models may be a means to determine whether there are non-threatened or unclassified species that share the characteristics of threatened species, however there are no data on which model might be most appropriate or whether multiple models should be used. In this paper, three types of statistical models, namely regression trees, logistic regression and discriminant function analysis are compared using data on the ecological characteristics of Finnish lepidopterans (butterflies and moths). Overall, logistic regression performed slightly better than discriminant function analysis in predicting species status, and both outperformed regression trees. Uncertainty in species classification suggests that multiple analyses should be performed and particular attention devoted to those species for which the methods disagree. Such standard statistical methods may be a valuable additional tool in assessing the likely threat status of a species where there is a paucity of abundance data.
In studies on genetic divergence, does the divergence value co-vary with the recommended actions ... more In studies on genetic divergence, does the divergence value co-vary with the recommended actions given in the paper's conclusion? Data incorporated: Articles from the journals Biological Conservation and Conservation Genetics published between 2007 and 2011 were reviewed for studies assessing genetic divergence that gave conservation recommendations for wild populations. Analytical methods: We used a general linear model with recommendation as the response variable to test this question. We then used a step procedure to eliminate variables that did not contribute significantly to the AIC value. The final model was compared with the constant-only model to test for significance. The majority of recommendations given in studies that include an analysis of genetic variation are informed by the divergence value estimated. However, the type of marker used and sample size, used here as a surrogate for estimation error, are significant factors influencing the recommendation. There is a high correlation between divergence values of nuclear and non-nuclear markers but recommendations appear to depend primarily on the analysis of nuclear markers.
The estimation of heritabilities and genetic correlations is based on the assumption that the tra... more The estimation of heritabilities and genetic correlations is based on the assumption that the trait distributions are normal. When the distributions are not normal it is advisable to transform the data to produce normality. However, it is possible that no suitable transformation can be found. The purpose of the present paper is to point out that the threshold model of quantitative genetics can be used as a generalized transformation. To utilize this method it is only necessary to divide the data at the median (approximately) and code the two halves as 0 and 1. Estimates can then be made using algorithms outlined herein. A simulation study shows that the threshold transformation gave unbiased estimates of the heritability and genetic correlation in all cases. The 95% con®dence limits correctly included the true heritability value in the required 95% of cases, while the estimated con®dence region for the genetic correlation was also correct provided that the geometric mean heritability was greater than approximately 0.15, a restriction that applied also to the normally distributed data. Con®dence intervals estimated from the non-normal data were consistently too small. The method is illustrated using data on the proportion of diapausing eggs produced by the cricket, Allonemobius socius.
Vibrational communication is known in some subterranean insects. Except for their use in sexual s... more Vibrational communication is known in some subterranean insects. Except for their use in sexual signaling, vibration behavior has rarely been reported. We report here four distinct types of substrate-based vibration behaviors in the mole cricket, Gryllotalpa orientalis, which are not associated with sexual signaling because of the occurrence of these behaviors in nymphs: (1) scraping with the forelegs; (2) foreleg taps (tapping with the forelegs); (3) palpal taps (tapping with the maxillary palpi); and (4) tremulation (back-and-forth movement of the whole body). Scraping is hypothesized to be used for the inspection of borrows. Foreleg taps are possibly informing nearby individuals of their presence, because it is never observed in solitary conditions. Palpal taps are rarely observed and its function is unknown. Tremulation is possibly related to avoidance of conspecific individual approaching and touching. The combination of the four vibration behaviors in the mole cricket may be unique among insects.
Many cryptic species have been discovered in various taxonomic groups based on molecular phylogen... more Many cryptic species have been discovered in various taxonomic groups based on molecular phylogenetic analyses and mating experiments. Some sympatric cryptic species share equivalent resources, which contradicts the competitive exclusion principle. Two major theories have been proposed to explain the apparent lack of competitive exclusion, i.e. niche-based coexistence and neutral model, but a conclusive explanation is lacking. Here, we report the co-occurrence of cryptic spider wasp species appearing to be ecologically equivalent. Molecular phylogenetic analyses and mating experiments revealed that three phylogenetically closely related species are found sympatrically in Japan. These species share the same resources for larval food, and two of the species have the same niche for nesting sites, indicating a lack of competitive exclusion. This evidence may suggest that ecologically equivalent species can co-occur stably if their shared resources are sufficiently abundant that they can...
In studies on genetic divergence, does the divergence value co-vary with the recommended actions ... more In studies on genetic divergence, does the divergence value co-vary with the recommended actions given in the paper's conclusion? Data incorporated: Articles from the journals Biological Conservation and Conservation Genetics published between 2007 and 2011 were reviewed for studies assessing genetic divergence that gave conservation recommendations for wild populations. Analytical methods: We used a general linear model with recommendation as the response variable to test this question. We then used a step procedure to eliminate variables that did not contribute significantly to the AIC value. The final model was compared with the constant-only model to test for significance. The majority of recommendations given in studies that include an analysis of genetic variation are informed by the divergence value estimated. However, the type of marker used and sample size, used here as a surrogate for estimation error, are significant factors influencing the recommendation. There is a high correlation between divergence values of nuclear and non-nuclear markers but recommendations appear to depend primarily on the analysis of nuclear markers.
Many sexual differences are known in human and animals. It is well known that females are superio... more Many sexual differences are known in human and animals. It is well known that females are superior in longevity, while males in athletic performances. Even though some sexual differences are attributed to the evolutionary tradeoff between survival and reproduction, the aforementioned sex differences are difficult to explain by this tradeoff. Here we show that the evolutionary tradeoff occurs among three components: (1) viability, (2) competitive ability and (3) reproductive effort. The sexual differences in longevity and athletic performances are attributed to the tradeoff between viability (survival) and competitive ability that belongs to the physical makeup of an individual, but not related to the tradeoff between survival and reproduction. This provides a new perspective on sex differences in human and animals: females are superior in longevity and disease recovery, while males are superior in athletic performance. T here are many sex differences in humans and animals 1 . The most well-known biological sex difference is sex-specific survivorship and longevity (life span or life expectancy at birth), where females live longer than males on average 2-4 . Another well-known gender difference is athletic performance in many sports, where males are usually superior in most comparable games 5 . These sex differences are suspected to have originated from two mechanisms: different functions associated with the sexual organs and optimality differences between sexes 1 . Examples of the former are various sex-specific traits such as menstrual periods, pregnancy and breast-feeding in females and ejaculation in males. The latter comprise various evolutionary (optimality) tradeoffs between individual survival and reproduction. The cost of reproduction in iteroparous (multiple bouts of reproduction) animals is a typical example of such tradeoffs 6,7 . However, some sex differences in humans are still difficult to explain by either the tradeoff between survival and reproduction, or by the sex-specific traits. We still have no clear scientific basis for these sex differences. Here we discuss a tradeoff between viability (survival) and competitive ability in the physical makeup of an individual. Because competitive ability is an important factor for mate acquisition for males, competitive ability in the form of male-male combat is also considered a cost of reproduction . In these cases, we often find sexual dichotomy in body size or the size of a body part. However, this tradeoff is distinctively different from the tradeoff between survival and reproduction, and is better explained under sexual selection (either mate choice or mating competition). Because males also allocate their efforts to reproduction, such as male sexual organs and male parental/family care, males also allocate the reproductive investment, as females. The sex-specific differences in survival and longevity, and athletic performance can be explained by the difference in a tradeoff between viability and competitive ability. Because of the costs of giving birth (labor) and/or parental care, female reproductive success is more sensitive to survivorship than males, while male reproductive fitness is more determined by mate competition . Because mate competition is usually contest competition, a high athletic ability is advantageous for mate competition in males. To explain these sex-specific differences we first build an allocation model of individual effort (energy) among three major components: (1) viability, (2) competitive ability, and (3) reproductive effort. Next, we consider the tradeoff between viability and competitive ability, the first two components of which are related to the physical
We experimentally tested a series of hypotheses proposed by Masaki (1979Masaki ( , 1986) ) for th... more We experimentally tested a series of hypotheses proposed by Masaki (1979Masaki ( , 1986) ) for the evolution of ovipositor length in crickets. Female crickets use the ovipositor to bury eggs in the soil, where it was hypothesized to protect their eggs from desiccation, cold and other disturbance. However, we found no effect of depth on the overwinter survival of eggs of three species of Nemobiinae. The probability of hatchlings reaching the soil surface was negatively correlated with depth documenting a significant cost to females laying eggs deep in the soil. Hatchling survival may be an important agent of selection on ovipositor length in habitats of different soil moistures. Hatchling survival in the soil was also correlated with body size, which may impose a constraint on egg-size fecundity trade-offs. Females of a bivoltine population of Allonemobius socius lay eggs at shallower depths when reared under summer compared to fall conditions and, therefore, may be able to respond to selection through behavioral plasticity when morphological adaptation is constrained by allometry.
A model is presented which demonstrates that a stable polymorphism for dispersal tendency can be ... more A model is presented which demonstrates that a stable polymorphism for dispersal tendency can be generated under a wide range of conditions. These conditions include both different genetic models and different "dispersal probability" functions. It is shown that individual selection for or against dispersers may result in a stable polymorphism which depresses population numbers and prevents population fitness from being maximized. Changes in the genotypic probabilities of dispersal may lead to very large changes in other parameters both with regard to their means and their spatial distribution. The effect of increasing environmental stability does not effect the proportion of dispersers maintained in the population in identical ways; the effect depends upon the parameter altered and the genetic model used.
Clinal variation in life histories can be genetically based, resulting from selection imposed by ... more Clinal variation in life histories can be genetically based, resulting from selection imposed by different environments, or it may be due to the differential expression of phenotypically plastic traits. We examined the cline in voltinism in the egg-diapausing cricket Allonemobius socius, with populations spanning the switch from a univoltine to a bivoltine phenology. A common garden experiment was employed, using environments that mimicked photoperiod and temperature conditions found in the field. There were only small differences in development time among populations, and the difference in phenology observed in the field is likely due to clinal variation in the length of the growing season. We found large genetically-based differences in the reaction norm for egg diapause that were further magnified by environmental cues. The synergism of genetic and environmental effects was an example of cogradient selection. In the zone of transition between phenologies, voltinism appeared to be a conditional strategy, rather than a genetic polymorphism. First-generation females from this area can lay either direct-developing or diapause eggs depending on the likelihood that a second generation will have sufficient time to develop. For this species, the cline in voltinism is the result of a combination of environmental effects on development, and genetic and environmental influences on egg diapause propensity.
Aluminium chamber bases were pressed 10 cm into the sediment to isolate square patches of sea flo... more Aluminium chamber bases were pressed 10 cm into the sediment to isolate square patches of sea floor 50 £ 50 cm. Sixteen chamber bases were established in close proximity at a depth of 6 m. Echinocardium were either added or removed from the bases to create experimental treatments with 0, 4, 8 or 16 urchins per chamber. The following morning, chamber lids (8 clear and 8 opaque) with non-directional water stirrers were fitted, enclosing about 25 l of bottom water. The light-dark treatment was interspersed equally across the urchin density treatment in a randomized block design. Chamber water was sampled near midday at 1.5-2 h intervals (exact times noted in each instance), providing the raw data for flux calculations 24 h after Echinocardium density manipulations. Bottom water external to the chambers was also sampled at each interval, and light and dark bottles were established just above the seabed at time ¼ 0 on the day of sampling. Dissolved oxygen was measured within minutes of collection (YSI model 5730 BOD bottle probe) and water samples were filtered immediately thereafter (1.1 mm pore size Whatman GF/C glass fibre filter). All samples were kept in darkness, and stored frozen until analysis. Analysis for ammoniacal nitrogen (NH 4 -N), nitrate-plus-nitrite nitrogen (NO x -N) and dissolved reactive phosphorus (DRP) used standard methods for sea water 29 on an AlphKem series 500 air-segmented continuous flow auto-analyser; detection limits ,0.1 mmol l 21 for N and P. To characterize features of the sediment column that could potentially affect pore water chemistry and flux chamber measurements, several types of sediment samples were collected from each chamber at the end of each experiment. Two surface sediment samples (,30 g scrapes to 2 cm depth) were collected, one for chlorophyll a analysis and one for organic matter content and sediment texture analysis. Chlorophyll a was extracted from sediment by boiling in 95% ethanol and analysed spectrophotometrically 30 . Organic matter content was assessed by % sediment mass lost following combustion (% loss on ignition, LOI). Sediment texture was assessed by standard sieve and pipette techniques after removal of organic matter (digestion in 9% hydrogen peroxide). Water content in the upper 5 cm of sediment was determined from one 2.4 cm diameter core per chamber from the difference in sample wet weight and dry weight. Macrofauna were collected with one 10 cm diameter, 13 cm deep core taken from the centre of each chamber base. Macrofauna were sieved on a 500 mm mesh sieve and preserved in 70% isopropyl alcohol þ rose bengal for later sorting and identification. When all sediment samples had been collected, the entire area enclosed by each chamber base was excavated to a depth of approximately 5 cm in order to quantify all Echinocardium present at time ¼ end. Each experiment was analysed separately. Sediment and faunal variables were used as predictors of dissolved chemical fluxes in multiple regression models. Variables were eliminated by backward selection unless significant at a ¼ 0.15. Collinearity among predictor variables was avoided by examining variance inflation factors and condition indices. Homogeneity of variance was evaluated by plotting residuals versus predicted values, and normality was assessed via normal probability plots and Shapiro-Wilk tests on residuals, though no data transformations were required.
In birds with altricial young an important stage in the life history is the age at fledging. In t... more In birds with altricial young an important stage in the life history is the age at fledging. In this paper we use an approach proven successful in the prediction of the optimal age at maturity in fish and reptiles to predict the optimal age of fledging in passerines. Integrating the effects of growth on future fecundity and survival leads to the prediction that the optimal age at fledging is given by a function that comprises survival to maturity, the exponent of the fecundity‐body size relationship and nestling growth. Growth is described by the logistic equation with parameters, A, K and ti. Assuming that the transitional mortality curve can be approximated by the nestling mortality, Mn, the optimal fledging age, tf, is given by a simple formula involving the three growth parameters, nestling mortality (Mn) and the exponent (d) of the fecundity‐body size relationship. Predictions of this equation underestimate the true values by 11–16%, which is expected as a consequence of the tr...
To understand fully the process of evolution of quantitative traits it is necessary to be able to... more To understand fully the process of evolution of quantitative traits it is necessary to be able to estimate the genetic correlation and its associated standard error. At present, estimation methods are available only for relatively simple designs. An alternative procedure is to use the correlation of family means as an estimate of the genetic correlation. We evaluate the utility of the family mean method and that of the more general procedure, the jackknife. The family mean method is shown to be potentially very biased unless family sizes are very large ( 20), and therefore its general utility is questionable. However, the jackknife method does provide valid estimates of both the correlations (phenotypic and genetic) and their standard errors.
The estimation of heritabilities and genetic correlations is based on the assumption that the tra... more The estimation of heritabilities and genetic correlations is based on the assumption that the trait distributions are normal. When the distributions are not normal it is advisable to transform the data to produce normality. However, it is possible that no suitable transformation can be found. The purpose of the present paper is to point out that the threshold model of quantitative genetics can be used as a generalized transformation. To utilize this method it is only necessary to divide the data at the median (approximately) and code the two halves as 0 and 1. Estimates can then be made using algorithms outlined herein. A simulation study shows that the threshold transformation gave unbiased estimates of the heritability and genetic correlation in all cases. The 95% con®dence limits correctly included the true heritability value in the required 95% of cases, while the estimated con®dence region for the genetic correlation was also correct provided that the geometric mean heritability was greater than approximately 0.15, a restriction that applied also to the normally distributed data. Con®dence intervals estimated from the non-normal data were consistently too small. The method is illustrated using data on the proportion of diapausing eggs produced by the cricket, Allonemobius socius.
Three estimates of heritability are available from the half-sib pedigree design: the sire, dam an... more Three estimates of heritability are available from the half-sib pedigree design: the sire, dam and genotypic estimates. Because of its significantly smaller standard error, the genotypic estimate is preferred provided that there are no non-additive effects that inflate the estimate. I present two methods to test for such effects: these are a t-test of the paired sire and dam pseudovalues from the jackknife procedure and the likelihood ratio test from the animal model. Both methods are shown to be valid tests for significant dominance and/or maternal effects. SPLUS coding for the implementation of the jackknife method is provided. Unless sample sizes are very large, the power of the tests is low and hence caution is advised in the use of the genotypic estimate following a nonsignificant test. An approximate power analysis can be done using the data from the jackknife method but the estimated power is typically a substantial underestimate of the true power and its use is not recommended.
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Papers by Derek Roff